1. Field of the Invention
The present invention pertains generally to alarm and security systems and particularly to remote alarm systems, such as those associated with automobiles.
2. Prior Art
A wide variety of vehicle alarm devices are known in the prior art and include door opening alarms, motion detectors and the like. Several of these employ transmitter/receiver systems. In U.S. Pat. No. 3,893,069, for example, a tone generator produces a signal transmitted from a transmitter when a compartment of the vehicle is opened. The operator of the vehicle has a receiver which will pick up the transmitted signal. The receiver can be a walkie-talkie and the received tone indicate tampering with the vehicle. In U.S. Pat. No. 3,703,703, a vehicle has a transmitter, coupled to the interior dome light, and it sends out a signal upon tampering with the ignition.
The operator of the latter vehicle can wear a bracelet containing a receiver. Another transmitter/receiver car security device is disclosed in U.S. Pat. No. 3,703,714. None of these systems, for example, will activate the alarm function, if someone is able to disconnect the car battery without activating a hood switch alarm. This is not very difficult to do, particularly if a thief plans ahead.
Continuous transmission devices such as U.S. Pat. No. 4,110,738 involve very complex coding schemes that are expensive and susceptible to generating false alarms. Also, a wide variety of separate back-up circuits exist as are discussed in U.S. Pat. No. 4,319,230.
Some devices such as that disclosed in U.S. Pat. No. 4,523,178 comprise a transmitter carried by an operator and a receiver mounted in several vehicles responsive to an encoded signal for activating a horn o other alarm for personal safety. A mechanism for disabling the ignition is physically associated with a receiver receptacle in a particular vehicle.
In U.S. Pat. No. 4,658,237, a vehicle intrusion alarm system broadcasts an alarm signal on the citizens band frequency. Further, a group of ganged-thumbwheel switches are used to provide a personal coding scheme to disable the transmitter when an authorized operator is in the vehicle. The alarm function is enabled by sensing a change in the vehicle system's voltage magnitude greater than a preselected tolerable maximum. Time-delay circuitry is used to provide for no alarm during authorized entry and exit time periods. Importantly, the transmitter broadcasts only during an alarm-sensing function. Accordingly, a transmitter failure does not itself indicate an alarm. That is to say, there is no "fail-safe" provision in this device.
The devices in the prior art are unsatisfactory for a number of reasons. First, the intrusion/security systems are often difficult to install and, if it is done professionally, expensive to install. These systems are susceptible to tampering by accessing the wire runs or sensors. Secondly, the devices are generally not portable. By installing the devices in a particular vehicle it is generally difficult or impossible to transfer the system from one vehicle to another. Thirdly, the other known alarms do not claim protection against simply towing the car away. Thus, if the vehicle is out of the range of the transmitter, no alarm is possible. The present invention will set off an alarm once the transmitter is out of range. Fourthly, the present invention employs a continuous transmission and thus if power is lost, the alarm will sound. This is far more satisfactory than the need for complex power back-up circuitry. Fifthly, the present invention specifically protects against false alarms due to momentary power interruptions. Sixthly, continuous transmission devices employ complex coded signals which increase the likelihood of false alarms. Finally, the present invention employs a fail-safe design: if either the power supply fails or there is a circuit component failure, the alarm will be activated.
None of the devices in the prior art are completely satisfactory and therefore, only a device in accordance with the present invention meets all of the requirements for a safe, inexpensive and reliable intrusion security alarm system.